The laboratory assessment of enamel erosion: a review

Preventive effect of different toothpastes on enamel erosion: AFM and SEM studies

The aim of the present in vitro study was the evaluation of new formulation toothpastes on preventing enamel erosion produced by a soft drink (Coca Cola), using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fifty enamel specimens were assigned to 10 groups of 5 specimens each. 1: intact enamel, 2: enamel + soft drink, 3: intact enamel + BioRepair Plus-Sensitive Teeth, 4: enamel + soft drink + BioRepair Plus-Sensitive Teeth, 5: intact enamel + BioRepair Plus-Total Protection, 6: enamel + soft drink + BioRepair Plus-Total Protection, group 7: intact enamel + Sensodyne Repair & Protect, 8: dentin + soft drink + Sensodyne Repair & Protect, 9: intact dentin + Colgate Sensitive Pro Relief, 10: dentin + soft drink + Colgate Sensitive Pro Relief. The surface of each specimen was imaged by AFM and SEM. The root mean-square roughness (Rrms ) was obtained from the AFM images and the differences in the averaged values among the groups were analyzed by ANOVA test. Comparing groups 4, 6, 8, 10 (soft drink + toothpastes) Colgate Sensitive Pro Relief promoted enamel remineralization, while BioRepair Plus-Sensitive Teeth, Biorepair Plus-Total Protection and Sensodyne Repair & Protect provided lower effectiveness in protecting enamel against erosion.

SIGNIFICANCE

the use of new formulation toothpastes can prevent enamel demineralization.

The role of different toothpastes on preventing dentin erosion: an SEM and AFM study®

The aim of the present in vitro study was the evaluation of new formulation toothpastes on preventing dentin erosion produced by a soft drink (Coca Cola®), using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fifty dentin specimens were divided in treatment and control halves and were than assigned to 5 groups of 10 specimens each: group 1a: intact dentin, group 1b: dentin + soft drink, group 2a: intact dentin + Biorepair Plus-Sensitive Teeth®, group 2b: dentin + soft drink + Biorepair Plus-Sensitive Teeth®, group 3a: intact dentin + Biorepair Plus-Total Protection®, group 3b: dentin + soft drink + Biorepair Plus-Total Protection®, group 4a: intact dentin + Sensodyne Repair & Protect®, group 4b: dentin + soft drink + Sensodyne Repair & Protect®, group 5a: intact dentin + Colgate Sensitive Pro Relief®, group 5b: dentin + soft drink + Colgate Sensitive Pro Relief®. The surface of each specimen was imaged by AFM and SEM. Comparing specimens of group a and b (no demineralization and demineralization), a statistically significant difference (p < 0.01) in Rrms values was registered. Comparing b groups, all the analyzed toothpastes tended to remineralize the dentine surface in different extent. Biorepair Plus-Total Protection® and Sensodyne Repair & Protect® provided higher protective effect against dentin demineralization.

Analysis of dentin/enamel remineralization by a CPP-ACP paste: AFM and SEM study

The aim of the present in vitro study was the evaluation of a CPP-ACP paste on preventing dentin/enamel erosion produced by a soft drink; Atomic Force Microscopy and Scanning Electron Microscopy were used. Eighty extracted human incisors free of caries were selected and divided into four groups (each divided in two subgroups); group 1a: intact dentin; group 1b: dentin + soft drink; group 2a: intact dentin + CCP-ACP paste; group 2b: dentin + soft drink + CCP-ACP paste; group 3a: intact enamel; group 3b: enamel + soft drink; group 4a: intact enamel + CCP-ACP paste; group 4b: enamel + soft drink + CCP-ACP paste. The CPP-ACP paste was applied for 3 min at 0, 8, 24, and 36 h. The surface of each dentin/enamel specimen was imaged by AFM (Rrms values were registered) and SEM. A statistical significant difference was recorded between groups 1b (dentin + soft drink) and 2b (dentin + soft drink + CCP-ACP paste) and between groups 3b (enamel + soft drink) and 4b (enamel + soft drink + CCP-ACP paste), suggesting that treatment of the specimens with the CPP-ACP paste had a protective effect on enamel demineralization, which was more evident for enamel specimens. Under the limitations of the present in vitro study, it can be concluded that the application of a CPP-ACP paste is effective on preventing dentin/enamel erosion produced by a soft drink.

A Nanomechanical Investigation of Three Putative Anti-Erosion Agents: Remineralisation and Protection against Demineralisation

An increasing interest in dental erosion as a clinical and scientific phenomenon has led to concerted efforts to identify agents which might protect against erosion. In this study, nanoindentation was used to investigate inhibition of erosive enamel demineralisation over time scales with direct clinical relevance. Nanohardness of polished human enamel specimens (n = 8 per group) was measured at baseline (B), after demineralisation (D1: citric acid, 0.3% w/v, pH3.20, 20s), after treatment (T), and after a second demineralisation (D2: as above). Data were analysed using repeated measures ANOVA. All specimens exhibited a similar reduction in nanohardness B-D1 in the range 35.2-39.5%. The positive control solution (saturated hydroxyapatite solution) and 4500 mg/L fluoride as NaF significantly increased nanohardness D1-T by 19.9% and 24.1%, respectively, whereas 1400 mg/L fluoride as NaF, casein phosphopeptide-amorphous calcium phosphate mousse and negative control (deionised water) had no significant effect. Nanohardness at D2 was indistinguishable for all groups, with total reduction in nanohardness B-D2 of 31.6% (4500 mg/L fluoride), 35.2% (positive control), 39.9% (1400 mg/L fluoride), 42.4% (negative control), and 43.7% (CPP-ACP product). In summary, 4500 mg/L fluoride significantly increased the nanohardness of previously demineralised enamel and resulted in the smallest total reduction in nanohardness but there were few statistically significant differences among the groups.

Spectrally enhanced imaging of occlusal surfaces and artificial shallow enamel erosions with a scanning fiber endoscope

An ultrathin scanning fiber endoscope, originally developed for cancer diagnosis, was used to image dental occlusal surfaces as well as shallow artificially induced enamel erosions from human extracted teeth (n=40). Enhanced image resolution of occlusal surfaces was obtained using a short-wavelength 405-nm illumination laser. In addition, artificial erosions of varying depths were also imaged with 405-, 404-, 532-, and 635-nm illumination lasers. Laser-induced autofluorescence images of the teeth using 405-nm illumination were also obtained. Contrast between sound and eroded enamel was quantitatively computed for each imaging modality. For shallow erosions, the image contrast with respect to sound enamel was greatest for the 405-nm reflected image. It was also determined that the increased contrast was in large part due to volume scattering with a smaller component from surface scattering. Furthermore, images obtained with a shallow penetration depth illumination laser (405 nm) provided the greatest detail of surface enamel topography since the reflected light does not contain contributions from light reflected from greater depths within the enamel tissue. Multilayered Monte Carlo simulations were also performed to confirm the experimental results.

Application of the specular and diffuse reflection analysis for in vitro diagnostics of dental erosion: correlation with enamel softening, roughness, and calcium release

We present assembly and application of an optical reflectometer for the analysis of dental erosion. The erosive procedure involved acid-induced softening and initial substance loss phases, which are considered to be difficult for visual diagnosis in a clinic. Change of the specular reflection signal showed the highest sensitivity for the detection of the early softening phase of erosion among tested methods. The exponential decrease of the specular reflection intensity with erosive duration was compared to the increase of enamel roughness. Surface roughness was measured by optical analysis, and the observed tendency was correlated with scanning electron microscopy images of eroded enamel. A high correlation between specular reflection intensity and measurement of enamel softening (r(2) ≥ -0.86) as well as calcium release (r(2) ≥ -0.86) was found during erosion progression. Measurement of diffuse reflection revealed higher tooth-to-tooth deviation in contrast to the analysis of specular reflection intensity and lower correlation with other applied methods (r(2) = 0.42-0.48). The proposed optical method allows simple and fast surface analysis and could be used for further optimization and construction of the first noncontact and cost-effective diagnostic tool for early erosion assessment in vivo.

Susceptibility of enamel treated with bleaching agents to mineral loss after cariogenic challenge

Objectives. Controversial reports exist whether bleaching agents cause a susceptibility to demineralization. The aim of this study was to compare the calcium loss of enamel treated with different bleaching agents and activation methods. Method and Materials. The specimens obtained from human premolars were treated in accordance with manufacturer protocols; 10% carbamide peroxide, 38% hydrogen peroxide light-activated, 38% hydrogen peroxide laser-activated, and no treatment (control). After cariogenic challenge calcium concentrations were determined by Inductively Coupled Plasma Mass Spectrometry. Results. No differences were found between the calcium loss of the laser-activated group and 10% carbamide peroxide group (p > 0.05). However, the differences between laser-activated and control groups were statistically significant (p < 0.05). The differences between 10% carbamide peroxide and the control group were not significant (p > 0.05). On the other hand, the light-activated group showed a significantly higher calcium loss compared with the other groups (p < 0.05). Conclusions. The results show that bleaching agents may cause calcium loss but it seems to be a negligible quantity for clinical aspects.

Studies on a novel combination polymer system: in vitro erosion prevention and promotion of fluoride uptake in human enamel

OBJECTIVES

Firstly, determine the effect of pre-treating sound human enamel with a hydrosoluble combination polymer system (TriHydra™) comprising 0.20% carboxymethylcellulose, 0.010% xanthan gum and 0.75% copovidone, alone or in combination with fluoride, on in vitro erosion by citric acid. Secondly, investigate the effect of the polymers on fluoride uptake by incipient erosive lesions.

METHODS

Study 1: Sound enamel specimens were treated (60s, 20°C, 150 rpm) with either (i) deionised water, (ii) polymers in deionised water, (iii) 300 mg/L fluoride or (iv) polymers in 300 mg/L fluoride. Specimen groups (n=5) were then immersed in 1.0% citric acid (pH 3.8, 300 s, 20°C, 50 rpm) and non-contact profilometry was used to determine surface roughness (Sa) and bulk tissue loss. Study 2: Incipient erosive lesions were similarly treated with (i)-(iv). Dynamic Secondary Ion Mass Spectrometry (DSIMS) was then used to determine the fluoride depth-distribution.

RESULTS

Study 1: Mean±SD Sa and erosion depths for treatment groups (i)-(iv) were (a)657±243, (b)358±50, (c)206±72, (d)79±16 nm and (a)19.73±8.70, (b)2.52±1.34, (b)0.49±0.34 and (b)0.31±0.21 mm respectively (matching superscripts denote statistically equivalent groups). Study 2: Lesions treated with (iii) and (iv) exhibited similar fluoride penetration depths (∼ 60 μm). Mean fluoride intensity ratios based on F/(F+P) at 1 μm for treatment groups (i)-(iv) were (a)0.010±0.004, (a)0.011±0.004, (b)0.803±0.148 and (c)0.994±0.004 respectively.

CONCLUSIONS

The combination polymer system exhibited anti-erosion efficacy in its own right. The polymer/fluoride admixture statistically significantly reduced Sa, however suppression of bulk tissue loss was not statistically significantly different versus either treatment alone. The presence of polymer appears to promote fluoride uptake by erosive lesions most noticeably in the first 6 μm.

Impact of acquired enamel pellicle modification on initial dental erosion

The acquired enamel pellicle that forms on the tooth surface serves as a natural protective barrier against dental erosion. Numerous proteins composing the pellicle serve different functions within this thin layer. Our study examined the effect of incorporated mucin and casein on the erosion-inhibiting potential of the acquired enamel pellicle. Cyclic acidic conditions were applied to mimic the erosive environment present at the human enamel interface during the consumption of soft drinks. One hundred enamel specimens were prepared for microhardness tests and distributed randomly into 5 groups (n = 20) that received the following treatment: deionized water, humidity chamber, mucin, casein, or a combination of mucin and casein. Each group was exposed to 3 cycles of a 2-hour incubation in human saliva, followed by a 2-hour treatment in the testing solution and a 1-min exposure to citric acid. The microhardness analysis demonstrated that the mixture of casein and mucin significantly improved the erosion-inhibiting properties of the human pellicle layer. The addition of individual proteins did not statistically impact the function of the pellicle. These data suggest that protein-protein interactions may play an important role in the effectiveness of the pellicle to prevent erosion.

A review of the structure of human and bovine dental hard tissues and their physicochemical behaviour in relation to erosive challenge and remineralisation

OBJECTIVES

This review sets out to examine the suitability of bovine hard dental material in lieu of human material when investigating dental erosion, to review the evidence for the major factors popularly attributed to dental erosion: pH, pKa, acid type, erosion duration, temperature and stirring rate as well as examine the case for the use of fluoride in an anti-erosion capacity.

DATA SOURCES

Published works were selected using online search software ICI Web of Knowledge and Pubmed, with key terms such as "enamel", "erosion" and "bovine AND human" and cross referenced with relevant papers cited in the indices.

RESULTS

The growing trend of dental erosion, coupled to legislative changes has precipitated a recent shortage of human enamel and dentine for experimental work. This in turn has resulted in the increasing use of cheap and readily available alternate supplies being sourced. This alternate supply principally originates from beef cattle under 20 months of age, under the assumption that bovine enamel and dentine will behave in a manner similar to human material. Recent experiments attempting to compare the physicochemical properties of these two species have shown that erosion is not simply a matter of bulk tissue loss resulting from acid exposure, but a multi-factorial event encompassing ever increasing and varied complexity of the inter-relationship between solvent and substrate.

CONCLUSIONS

Accurate data from the published literature regarding the comparative properties of human and bovine hard dental tissue remains scarce but consensus appears to accept the continuing use of bovine enamel as a substitute for human enamel. This lack of comparative data is further hampered by the lack of an established, standardised protocol with which to evaluate the two species. In addition, much debate remains regarding the significant principal factors responsible for dental erosion and ways to minimise the pathological manifestation.

In vitro demineralisation of the cervical region of human teeth

OBJECTIVE

The aim of this study was to investigate a possible role for demineralisation of the cervical region of human teeth in the development of non-carious cervical lesions (NCCLs).

MATERIALS AND METHODS

Freshly extracted human premolars were demineralised and prepared for nanoindentation and scanning electron microscope (SEM) observation. After 1 day or 2 days demineralisation in a solution of pH 4.5, specimens were embedded, cut and polished to 1 μm diamond paste. Nanoindentation was done at the cementum-enamel junction (CEJ) region with an interval of 30 μm, to develop mechanical properties maps. After the indentation, SEM with back-scatter detector was employed to observe the degree of demineralisation at the CEJ.

RESULTS

After 1 day and 2 days demineralisation, the mechanical properties of enamel and dentine at the CEJ decreased by ∼50% and ∼90%, respectively. SEM images illustrate that artificial demineralisation generated typical demineralised zones in enamel near the CEJ. Moreover, 2 days demineralisation penetrated the sound enamel at the CEJ, and the dentine beneath was undermined.

CONCLUSION AND SIGNIFICANCE

One day and 2 days demineralisation reduced the mechanical properties of teeth at the CEJ significantly. Demineralised enamel and dentine with low mechanical properties are prone to wear and abrasion. The findings of the investigation indicate that acid typical of that produced by dental plaque may compromise the mechanical properties of enamel and dentine at the CEJ to the extent that they would be susceptible to tooth brush abrasion, producing NCCLs.

Impact of two toothpastes on repairing enamel erosion produced by a soft drink: an AFM in vitro study

OBJECTIVES

The aim of the present in vitro study was the evaluation of two toothpastes (Sensodyne Pronamel and Biorepair Plus on repairing enamel erosion produced by a soft drink (Coca Cola), using Atomic Force Microscopy (AFM).

METHODS

Fifty extracted human central incisors free of caries were selected and divided in a treatment and a control half; they were kept in artificial saliva during whole experimentation. The treatment halves were divided into five groups; group 1: demineralization with soft drink; group 2: demineralization with soft drink + Pronamel; group 3: demineralization with soft drink + Biorepair Plus; group 4: intact enamel + Pronamel; group 5: intact enamel + Biorepair Plus. Specimen demineralization was carried on in 4 intervals of 2 min. In groups 2, 3, 4, and 5 the toothpastes were applied for 3 min at 0, 8, 24 and 36 h. The surface of each specimen was imaged by AFM and R(rms), root-mean-square roughness, and Maximum Depth of the cavities were registered.

RESULTS

Amongst treatment specimens of groups 1, 2, and 3 a statistically significant difference (P<0.01) in R(rms) and Maximum Depth values was registered: the toothpastes reduced enamel demineralization. No statistical differences in R(rms) values were registered between the two toothpastes.

CONCLUSIONS

The toothpastes tested (Pronamel and BioRepair Plus) offer a degree of protection from erosive drinks.

Protective effect on enamel demineralization of a CPP-ACP paste: an AFM in vitro study

OBJECTIVES

The aim of the present in vitro study was the evaluation of a CPP-ACP paste (Tooth Mousse) on preventing dental erosion produced by a soft drink (Coca Cola), using Atomic Force Microscopy (AFM).

METHODS

Thirty extracted human central incisors free of caries were selected and divided in a treatment and a control half. The treatment halves were divided in three groups-group 1: demineralization with soft drink (4 intervals of 2 min); group 2: demineralization with soft drink (4 intervals of 2 min) plus Tooth Mousse; group 3: intact enamel plus Tooth Mousse. In groups 2 and 3 Tooth Mousse was applied for 3 min at 0, 8, 24 and 36 h. The surface of each specimen was imaged by AFM and R(rms) values were registered.

RESULTS

Among treatment specimens of groups 1 and 2, a statistically significant difference (P<0.01) in R(rms) values was registered: treatment of the specimens with CPP-ACP paste had a protective effect on enamel demineralization. In group 3 no statistically significant difference was registered between exposed and not exposed halves of the specimens.

CONCLUSIONS

The use of a CPP-ACP paste had a protective effect on enamel demineralization in an in vitro model.

Effects of Er:YAG laser irradiation and manipulation treatments on dentin components, part 2: energy-dispersive X-ray fluorescence spectrometry study

The effects of laser etching, decontamination, and storage treatments on dentin components were studied by energy-dispersive X-ray fluorescence spectrometry (EDXRF). Thirty bovine incisors were prepared to expose the dentin surface and then divided into two main groups based upon the decontamination process and storage procedure: autoclaved (group A, n=15) or stored in aqueous thymol solution (group B, n=15). The surfaces of the dentin slices were schematically divided into four areas, with each one corresponding to a treatment subgroup. The specimens were either etched with phosphoric acid (control subgroup) or irradiated with erbium-doped yttrium-aluminum-garnet (Er:YAG) laser (subgroups: I-80 mJ, II-120 mJ, and III-180 mJ). Samples were analyzed by micro-EDXRF, yielding three spectra for each area (before and after treatment). Surface mappings covering an area of 80x60 points with steps of 20 mum were also performed on selected specimens. The amount of Ca and P in group A specimens decreased significantly (P<0.05) after the acid etching and the CaP ratio increased (P<0.001). Er:YAG laser-etching using lower laser energies did not produce significant changes in dentin components. The mapping data support the hypothesis that acid etching on dentin produced a more chemically homogeneous surface and thus a more favorable surface for the diffusion of adhesive monomers.

The enamel softening and loss during early erosion studied by AFM, SEM and nanoindentation

Enamel dissolution occurs when it contacts with acids produced by plaque bacteria, foods or drinks. There have been numerous and varied studies quantifying and characterizing the rate, extent and chemical aspects of enamel erosion; however, there is still hot debate about the amounts of enamel softening and loss. The objective of this study was to measure the enamel erosion process with high accuracy. Native third molars were partly eroded in citric acid (pH = 3.8) with some domains protected by a Ti coating layer. The surface morphology and structures before and after exposure to citric acid for different time periods were studied by AFM, SEM and nanoindentation, respectively. Based on this, the functions between the amounts of enamel softening, loss and erosion time were established for the first time. It was demonstrated that AFM, SEM and nanoindentation were suitable for measuring the early stages of enamel demineralization qualitatively and quantitatively.

Influence of beverage composition on the results of erosive potential measurement by different measurement techniques

The influence of beverage composition on the measurement of erosive potential is unclear. The aim of this study was to evaluate whether beverage composition influences the measurement of erosive potential and to evaluate the influence of exposure in small and large volumes. Eleven beverages were included: water (control), 3 alcopops, 2 beers and 5 soft drinks. For each beverage 15 bovine enamel samples were used: 5 for chemical and 10 for profilometric analysis. After exposure to the beverages (63 min) the resulting solutions were analyzed for Ca and inorganic phosphorus (P(i)) content. The samples for optical profilometry were submersed sequentially in 500 ml or in 1 ml of the drinks for 3, 6, 9, 15 and 30 min (total 63 min). For some of the beverages high baseline concentrations of Ca (energy drink) or P(i) (cola drink, cola lemon drink, beer, beer lemon) were found. Some of the beverages showed a good correlation between the chemical methods. Profilometry (both for 1 and 500 ml) showed generally lower enamel losses than the chemical methods. Lower enamel losses were found for the profilometry 1 ml compared to the profilometry 500 ml only for the cola drinks. It can be concluded that the composition of the beverages had a significant effect on the determination of the erosive potential with chemical analyses. Drink composition also influenced the effect of small versus large exposure volumes, indicating the need for standardization of exposure parameters.

An in vitro investigation of the effect of some analgesics on human enamel

The sale of over-the-counter pain relief medication has increased dramatically in recent years, and typically amounts to several hundred thousands of pounds per year in the UK. Many soluble analgesic preparations contain citric acid, and it has been suggested that these formulations may cause dental erosion. The aim of this study was to investigate the effect of some over-the-counter analgesics on tooth surface loss from human enamel. Six commonly available analgesics were chosen for this study and the effect of immersing unerupted human enamel was examined using non-contact optical profilometry. Two of the six analgesics investigated caused no detectable erosion (Boots soluble aspirin and Anadin Extra). Three caused statistically significant enamel erosion, but this was very slight and is thought to be clinically insignificant (Alka Seltzer, Panadol and Solpadeine). Only one analgesic caused possible potentially clinical significant enamel erosion. Further studies are needed to determine whether Aspro causes clinically significant enamel erosion.

The relationship between enamel softening and erosion caused by soft drinks at a range of temperatures

OBJECTIVES

Investigations of the erosive potential of soft drinks are usually performed at room or body temperature, but drinks are more frequently served chilled, with ice, or hot. Since the rate of chemical reactions usually increases with temperature, it is predicted that erosion is more severe at high temperatures and reduced at low temperatures. The aim of this study was to investigate the correlation between enamel softening, enamel erosion, and temperature.

METHODS

Atomic force microscopy nanoindentation and non-contact optical profilometry were used to assess changes in enamel nanomechanical properties after 5 min and erosive material loss after 30 min exposure to two different non-carbonated soft drinks at 4, 25, 50 and 75 degrees C.

RESULTS

For one drink (Robinson's Original Juice Drink), there was a statistically significant difference between nanomechanical properties and erosion depth at all temperatures, with softening and erosion increasing with temperature. For another drink (Ribena ToothKind Juice Drink), there was a slight softening and virtually no material loss, and temperature had no statistically significant impact on erosion. There was a good linear correlation (R2 = 0.94) between nanomechanical properties and material loss.

CONCLUSIONS

The difference between the drinks can be explained by their composition. For the erosive drink, material loss increased, and nanohardness decreased, approximately linearly with temperature. The correlation between softening and erosion demonstrated that nanomechanical properties after very short erosion times can be considered a good predictor of bulk material loss after considerably longer erosion times.